The Group IV semiconductor materials enjoy wide acceptance as the materials of choice in a range of devices in numerous markets such as communications, computation, and energy. Currently, there is interest in using Group IV semiconductor nanoparticle materials in a wide range of components and devices.
For example, due to the luminescent properties of small nanoparticles, silicon and germanium nanoparticles have been contemplated for use in light-emitting applications, including use as phosphors for solid-state lighting, luminescent taggants for biological applications, security markers and related anti-counterfeiting measures. Other potential applications of Group IV semiconductor nanoparticles include a variety of optoelectronic devices, such as light-emitting diodes, photodiodes, photovoltaic cells, and sensors that utilize their unique optical and semiconductor properties. Because of the ability to produce colloidal forms of semiconductor nanoparticles, these materials offer the potential of low-cost processing, such as printing, for producing a variety of electronic devices that is not possible with conventional semiconductor materials. In that regard, tantamount to dispensing Group IV nanoparticle materials is not only the formulation of stable dispersions of the materials, which dispersions enable printing in a number of formats, but in formulations of inks which are suitable for the fabrication of a variety of optoelectric devices, such as photovoltaic devices.
In WO04068536A2 [Harting, et al.; International Patent Application No. WO2004IB00221, filing date Jan. 30, 2003] formulations of nanocrystalline silicon particles of about 30 nm in diameter, and formulated in a solvent-binder carriers are described. The nanoparticles were mixed with organic binders such as polystyrene in solvents such as chloroform to produce semiconductor inks that were printed on bond paper without further processing. In U.S. Patent Application Publication No. 2006/0154036 [Kunze, et al.; Ser. No. 11/373,696; filing date Mar. 10, 2006], composite sintered thin films of Group IV nanoparticles and hydrogenated amorphous Group IV materials are described. The Group IV nanoparticles are in the range 0.1 to 10 nm, in which the nanoparticles were passivated, typically using an organic passivation layer.
Additionally, a component in the ink formulation; a second cyclic Group IV compound, is a compound including organic ligands that are alkyl, aryl, or aralkyl ligands. In order to fabricate thin films from these organic passivated particles and carbon-containing cyclic compounds, the processing was performed at above 400° C. In both examples, significant amounts of organic materials are present in the inks used to fabricate Group IV thin film layers. Such organic-laden dispersions are known to be problematic in producing the well-accepted native Group IV semiconductor thin films known in the semiconductor industry.
U.S. Pat. No. 7,062,848 [Pan, et al.; Ser. No. 10/665,335; filing date Sep. 18, 2003] discloses a printable composition of nanoparticles composed of a liquid carrier, anisometric nanostructures, and in some embodiments, a stabilizing agent that reacts with the nanoparticles to produce a surface-attached ligand. The ligands are recited as being drawn from broad chemical classes, such as carboxylates, thiolates, alkoxides, alkanes, alkenes, alkynes, diketonates, siloxanes, silanes, germanes, hyroxides, hydrides, amides, amines, carbonyls, nitriles, aryl, and combinations thereof. Likewise, examples of the liquid carrier was drawn from broad chemical classes including hydrocarbons, alcohols, ethers, organic acids, esters, aromatics, amines, as well as water, and mixtures thereof. Though anisomeric silicon and germanium nanoparticles are recited as subject nanoparticles, there is no disclosure for how to prepare stable dispersions of such Group IV semiconductor nanoparticles, which dispersions are suitable for making a variety of optoelectric devices, such as photovoltaic devices. Moreover, two examples are given for preparation of printable compositions of zinc oxide; one of which is passivated using carboxylate compounds, and the other preparation of zinc oxide where the ligand is only described as hydrophilic for the purpose of being prepared as an aqueous dispersion.
In U.S. Patent Application Publication No. 2006/0237719 [Colfer, et al.; Ser. No. 10/533,291; filing date Oct. 30, 2003] though note is made of the problem of oxidation of Group IV semiconductor nanoparticles, nonetheless description is given for the preparation of Group IV semiconductor nanoparticles in aqueous dispersions containing about 30% of the surfactant polyethylene glycol (MW 200). In some embodiments, a capping ligand, such as octanol or a carboxylate terminal alkyl group is noted to assist in the dispersion of Group IV semiconductor nanoparticles in non-aqueous or aqueous solvents, though the preparation of dispersions of such capped Group IV semiconductor nanoparticles is not disclosed. Further, examples of the fabrication of a variety of optoelectric devices, such as photovoltaic devices, using such dispersions is not given.
Accordingly, there is a need in the art for the preparation of Group IV nanoparticle materials, and dispersions of such Group IV semiconductor nanoparticles materials that are suited for the fabrication of a variety of optoelectric devices, such as photovoltaic devices. Such dispersions are not only amenable to printing using a variety of techniques for a range of print dimensions ranging from sub-micron to meters, but enable the ready fabrication of semiconductor devices.